Fig. 4.

Endosomal and endogenously synthesized cholesterol is transported into mitochondria. A, C: Pregnenolone formation in intact, adherent F2-CHO (A) or F2-4-4-19 (C) cells grown in medium containing 5% LPDS and 50 µg/ml LDL for 48 h, then incubated in the presence (LDL→LDL) or absence (LDL→SF) of LDL in serum-free (SF) import medium for 24 h, or grown in medium containing 5% LPDS without LDL for 48 h, then incubated in the presence (LPDS→LDL) or absence (LPDS→SF) of LDL in serum-free import medium for 24 h. Pregnenolone was determined in import medium as ng pregnenolone per mg cell protein and is depicted as percentage of the average of the LDL→LDL incubation. B, D: Cholesterol biosynthesis in F2-CHO (B) or F2-4-4-19 (D) cells grown under the same conditions as in A and C with the addition of 1 µCi/ml [¹⁴C]acetate to the import medium. Cellular lipid extracts were separated by thin-layer chromatography, and radioactivity was counted in the band corresponding to unesterified cholesterol. Data are expressed as dpm per mg cell protein. All data are means ± SEM of three independent experiment in triplicate with two clones each F2-CHO and F2-4-4-19 cells (n = 18). * P < 0.05.